How does the fetus become a boy or a girl......
2007-03-21 08:35:47 · 11 answers · asked by Blondie 2 in Pregnancy & Parenting ➔ Pregnancy
it's pretty complicated, and certainly more so than just whether the chromosomes are XX or XY. there have been several genes identified that determine the *gender* of a foetus, some need to be *triggered* in order to take effect. i remember seeing a programme that explained that there needs to be a flush of a particular hormone in a particular 48 hr window during early pregnancy in order to trigger the development of male sexual characteristics even when the foetus is chromosomally *male*. so you can have a person who is genetically male, but has the sexual characteristics of a female... and vice versa.
http://www.hhmi.org/biointeractive/gender/
has an interactive thingy - click on the *gender testing of female athletes* link, and you'll get taken through an explanation of how this can happen.
these links have more technical information.
http://www.dukemednews.org/news/article.php?id=9664
http://www.scq.ubc.ca/?p=291
http://www.npr.org/templates/story/story.php?storyId=1046364
2007-03-21 09:16:51 · answer #1 · answered by Anonymous · 0⤊ 0⤋
There is a partcular segment found only on the Y chromosome (called the sex determining factor-Y) that is in control of releasing directing the baby to develop into a boy. Fetuses are at first gender asexual, their developing reproductive organs are caled gonads, neither specifially male or female. If and when the SDF-Y is activated, the DNA code directs the fetus to produce testosterone and the gonads develop into testes, and all the accompanying male parts result. In the abscence of SDF-Y, (as in the XX chromosome combination of girls) the gonads develop as ovaries and begin producing eggs, and a female system develops.
2007-03-21 16:05:07 · answer #2 · answered by Robin J. Sky 4 · 1⤊ 0⤋
The fetus doesn't need to "know" what to become. It is either a boy or girl the instant the baby is conceived...the sex organs just aren't visible yet.
The fetus then develops the appropriate genitalia determined by DNA. The fetus doesn't need to know how to do everything...it grows and develops on its own.
2007-03-21 15:40:47 · answer #3 · answered by LittleRoo 4 · 2⤊ 0⤋
A woman has eggs they contain an X chrosome
The guys have sperms that contain an X or an Y chromosome...
When an egg and a sperm meet they melt together..
Depending on what the sperm had as a chrosome it will become a boy or a girl...
XX = a girl
XY = a boy
2007-03-21 15:40:55 · answer #4 · answered by Princess 4 · 0⤊ 1⤋
The sperm have the chromosome to determine sex, so there are male and female sperm. The sex is already decided by which sperm fertilize the egg. The baby's sex organs in early development look the same. Once they start to develop, they become more distinguishable. Usually around 15 weeks.
2007-03-21 16:02:02 · answer #5 · answered by Melissa B 5 · 0⤊ 1⤋
They're called chromosomes... all eggs have female chromosomes (XX). A male's sperm cells are the determining factors when it comes to gender... men can produce both female (XX) and male (XY) sperm. If an XY sperm fertilizes the egg cell, then you've got a boy. If the XX sperm does it, then you've got a girl.
Keep this argument in mind when your folks keep bugging you for a grandchild of a particular gender. My mom kept asking me "Where's my granddaughter?!" and I kept saying, "Don't ask me, as my husband! All's I make is girls!"
2007-03-21 15:43:35 · answer #6 · answered by shoujomaniac101 5 · 1⤊ 1⤋
It doesn't have to know what to become, the sperm will take care of that, you either got xx or xy chromazomes, like a sun flower seed, how does it know to turn into a sunflower, its like a blueprint in every seed, and theres a blue print in every fetus. metaphorically ofcourse.
2007-03-21 15:45:47 · answer #7 · answered by doc 6 · 0⤊ 1⤋
The chromosomes either show up as xx which is a girl or xy as a boy! All girls give the x chromosome and the guys can give either one and that is what makes is a boy or girl!
2007-03-21 15:39:52 · answer #8 · answered by KValdez 2 · 1⤊ 1⤋
excuse me? a fetus doesnt know anything
2007-03-21 15:40:45 · answer #9 · answered by lucifer 1 · 1⤊ 0⤋
How about a free video all about it??
go here..
http://www.pbs.org/wgbh/nova/miracle/program.html
the program is broken into parts, you can watch it all, or scroll down to how sex is determined..
2007-03-21 15:43:22 · answer #10 · answered by ? 4 · 0⤊ 0⤋